Casting process



July 4, 1944. I J. D LEIQGHT ON I CASTING PROCESS 2 Sheets-Sheet l Filqd July 17, 1943 INVENTOR. J5%r/fl 16.25% 27 /2 BY I frog/wry: H

July 4,1944. ,J. D. LEIGHTON 2 CASTING PROCESS Filed July 17, 1945 2 Sheets-Sheet 2 IN VEN TOR.

J'Z n file ,4 TTO/ZNEXS J Patented July 4, 1944 UNITED STATES PATENT OFFICE CASTING PROCESS John D. Leighton, Port Huron, Mich. Application July 17, 1943, Serial No. 495,149

13 Claims.

The invention relates to casting of.metal by means of pressure, and it has particular relation to improvements in the art of making precision castings of fine grain structures.

While the invention hereinafter described has a more or less general application, it is particularly useful in the casting of intricately shaped and precise articles. It has been general practice, particularly in the fields of dentistry and jewelry, to form cavities by investing them in suitable investment compound by means of volatile models and then to force molten metal into the cavities after the models have been evaporated from the compound. This usually requires melting of the metal in a separate furnace or the like and then forcing the molten metal into the cavities.

One object of the present invention is to provide an improved combined method of melting and casting which is more eflicient and economical and which results in the production of castings at substantially lower cost than articles requiring intricate machine operations and is an improvement over other methods of casting since it saves time and materials. A

Another object of the invention is to provide an improved method of casting which avoids the use of melting crucibles and excessive exposure of the air to the molten metal.

- Another object of the invention is to save metal largely prevents oxidation of the metal and the undesirable elTects of it; and to provide a means of speedily melting the correct amount of metal in a minimum of time. i

Another object of the invention isto' save model waxing material by having the metal to be melted practically filling the major sprue cavity.

Other objects and advantages of the invention will become apparent from the following specification, the drawings relating thereto, and the claims hereinafter set forth.

For a better understanding of the invention reference may be had to the drawings, wherein:

Figure 1 is a cross-sectional view of casting apparatus employed in practicing one form of the invention;

Figure 2 is a cross-sectional view showing a mold which may be used for molding the metal into a combined wax and metal to be melted mould;

Figures 3 and 4 illustrate successive stages employed in the use of the apparatus shown by Figure 1;

Figure5 is a cross-sectional view similar to Figure 1 illustrating another form of apparatus employed in practicing a modified form of the invention;

Figure 6 is a cross-sectional view taken substan tially along the line i5 of Figure 4 Figure 7 illustrates apparatus used in ing still another form of the invention;

Figure 8 is a cross-sectional view taken substantially along the line 8-8 of Figure 7; and

Figure 9 is a view on the order of Figure '7 illustrating a difierent type of metal body which maybeused.

Referring to. Figure 1, the apparatus shown comprises a holder Ill constructed of a suitable investment compound, which is shown as mounted on a spindle ll so that the holder may be rotated. At its upper side the holder has a tapered recess, indicated at l2, and this recess receives a ring l3 constructed of high temperature resisting material and which may be inserted and removed from the recess. At its inner side the rin I3 is also tapered, as indicated at I4, and the cavity within the ring is adapted to receive an investment compound, indicated atl5. This investment compound may consist of any suitable material used in forming mold cavities for casting, purposes and similar investment compounds known in the field of dentistry for this purpose may be used.

According to one form of the present invention, a metal ring I1 is first formed from wire and this may be accomplished by automatic machinery which will form and sever one convolution of wire. Around this ring a series of forms and connect ing elements 2i are arranged in circumferentially distributed relation, and the latter, at their inner ends, join a coating of wax 22 on the ring. The forms, connecting elements and coating may be made from wax or other suitable volatile material having a suitable melting point, and they are applied to the ring by suitable molding equipment shown by Figure 2. This equipment comprises two mold parts 2i and 25 having complementary cavities adapted to shape the wax model about the ring. Preferably, the two parts will have their cavity surfaces treated to prevent sticking and the cavity for the ring will be sufliciently larger than the "latter so as to enable attaining a substantial coating of wax thereon. This coating acts to anchor the elements 2| on the ring and, additionally, the space left when the coating is melted and evaporated allows for expractic pansion of the metal when it is subsequently heated. An opening 26 is provided in part 24 through which molten wax may be forced into the space around the ring and into the cavities around the ring.

After the ring I! is thus provided with the de sired number of wax forms 20 attached thereto by the wax connecting elements 2| and coating 22 so as to form the model, the latter is removed from the mold and then is embedded within the investment compound l5 with the ring center on the spindle axis. The holder l0, ring 13 and investment compound l5 then may be placed in a furnace and heated sufllciently to melt and evaporate the wax or suitable model material being used, it being understood that the porosity of the compound will be sufficient to allow necessary evaporation. Evaporation of the wax leaves the ring I! in communication with mold cavities 21 by means 01 openings 28. Y

For melting the ring l1, an electrical induction coil 30 is used which melts the metal while it is in the investment compound, as will be readily understood. After the metal is melted, the holder Ill preferably may be withdrawn from the coil and then rotated about the axis of the latter, during which centrifugal force acts to iill the cavities in a substantially uniform manner. This molten metal moves into the openings 28 and then into the formed cavities 21 and rotation continues until the metal solidifies. During the outward movement of the metal any air or gas in the cavities may move through the compound, although it will be apparent that any air or gas also may flow past the molten metal and into the space formerly occupied by the ring. It will be appreciated that the amount of metal in the wire ring may be predetermined in accordance with the number and size of articles to be cast and that excess metal may be reduced to a minimum.

The wire ring I! in the coil 30 may be melted either by passing the coil over the holder or moving the holder into the coil and then separating them after a lapse of sumcient time to assure melting of the metal. It is also feasible to place the coil around the holder and then to rotate the holder while in the 'coil.

In any event. the wire is melted while embedded within the investment compound and is then forced centrifugally into the cavities. Thus, no separate melting of the metal and use of crucibles for pouring it into sprue openings is required. Furthermore, the melting and handling of the molten metal is effected while it is surrounded by investment compound in closely confining relation thereto and excessive exposure to air and hence oxidation of metal is practically eliminated. v

In the apparatus shown by Figure 5. a fire resisting clay or other holder 35 is provided which contains a non-melting refractory material 35 having a central projection 31. The investment compound in this instance is in the form of a block 38 having a central opening 39 receiving the projection 31. or, in other words, the invest-' ment compound is applied on the surface of the material 36 in surrounding relation to the projection 31. Any suitably strong investment compound could be used which would not require the use of an outer fire'clay ring, such as the ring l3 in Figure l, or, if desired, the compound could have its outer peripheral portion only sufficiently strong so as to hold the inner parts of the compound to ether when rotation, occurs or in the event fluid pressure is used to fill the moulds.

In this case, the metal ring indicated at 4| is in communication with form cavities 4| by means of communicating openings 42 and these may be formed in the manner reviously described; that is, by using wax or other suitable material and subsequently melting and evaporating the wax. Additionally, cavities of ball shape, as indicated at 44, may be provided at the inner end of each communicating opening 42, as best shown by Figure 6, and these likewise may be formed by rising wax forms and subsequently melting and evaporating the wax. In other words, each communicating opening 42 will join a ball shape recess through which the ring passes. Additionally, in this form of the invention small vents 4'Im-ay be provided which lead from the ring to the upper surface of the compound 38 so as to allow escape of gases if the porosity of the compound is not sufficient to let the gases escape. Perhaps in normal cases these vents are not required, but in the case of certain metals they may be desirable and it may be added that such vents, if desired, may be used in the apparatus shown by Figure 1. r

Upon melting of the wire by electrical induction in the manner previously described, the mol-. ten metal tends to collect in the ball shaped .recesses 44 so as to provide in eii'ect an individual sprue opening for each form cavity. Also, these ball shaped recesses 44 tend to locate the proper quantity of molten metal at the inner end of each opening 42 and thus to equally divide the molten metal.

After melting of metal, the holder 35 may be rotated, as previously described, so as to centrifugally force the metal outwardly into the form receiving cavities. It has been mentioned previously that the amount of metal may be predetermined and manifestly in the caseofeither Figure 1 or Figure '5, the ring may be larBe enough to fill not only the cavities 21 but also the openings", so as thereby to ensure filling of each cavity. The amount ofmetal also may be sufficient so that the openings 28 would be filled and a small amount of metal would be retained in the ring cavity and hence all of the articles cast would come out of the mold in connected relation to facilitate the rapid removal of castings from sprues. v

In the construction shown by Figures 7 and 8, a block of metal 50 is placed within investment compound 5| and, similarly to the structures already described, cavities 52 and communicating openings 53 may be formed by the use of wax or other suitable material. The metal then is melted by electrical induction in the manner previously specified, but instead of using centrii ugal force in this case, air or other fluid pressure is employed to force the metal outwardly into the cavities, it being understood that any air or gas in the cavities will'be allowed to escape from the cavities through the compound or through small vents, if required. This fluid presoutwardly into the cavities. In this case, a small vent could beprovided, if necessary, leading to the metal so as to allow enough atmospheric air to reach the melted metal to cavities.

The diilerent forms of the invention provide means for precision casting and to accomplish this result economically and efllciently with minimum waste of material. Furthermore, use of the invention avoids separate melting of the metal and handling thereof in crucibles and thus time and labor required are minimized. Furthermore, the handle of the molten metal and the melting of the metal within the investment compound avoids oxidation since the metal is practically excluded from contact with the air or at least oxidation is minimized. As a result, more perfect castings can be made.

'Although more than one form of the invention has been illustrated and described, it will be apparent to those skilled in the art that various modifications and changes may bemade without departing from the scope of the appended claims.

What is claimed is:

1. The method of casting which comprises placing and embedding a body of metal to be melted within an investment compound, forming one or more mold cavities within the compound and forming an opening leading from the cavity to the metal, and then melting the metal and causing the molten metal to flow through said opening into the mold cavity.

2. The method of casting which comprises placing and embedding a body of metal to be melted within an investment compound, forming one or more mold cavities within the compound and forming an opening leading from the cavity to the metal, then melting the metal, and then centrifugally forcing the metal into the cavity by rotating the compound.

3. The method of casting which comprises placing and embedding a ring of metal to be melted within an investment compound, forming one or more-mold cavities within the compound and forming an opening leading from the ring to the cavity, then melting the metal, and rotating the compound about the axis of the ring to centrifugally form the molten metal into the cavity.

4. The method of casting which comprises providing a body of metal to be melted, molding force it into the a form from material having a melting point' lower than the metal with such form corresponding in shape to the metal article to be cast, attaching the form to the metal body by means of a connecting element formed from said material, embedding the metal body, form and connecting element within aninvestment compound, melting and removing the material mentioned so as to leave a mold cavity connected to the metal body by a communicating opening, melting the metal body, and causing the molten metal to flow into the cavity.

5. The method of casting which comprises providing a ring of metal to be melted, molding forms from volatile material having a melting point lower than the metal with such. forms corresponding in shape to the articles to be cast. attaching said forms to the ring by means of connectors formed from said material, embedding the metal ring, forms and connectors within an investment compound, melting and evaporating said material, melting the metal ring,

and rotating the compound about the axis of the ring so as to centrifugally force the molten metal outwardly into the cavities.

6. The method of casting which comprises providing a body of metal to be melted, molding a form from volatile material having a melting point lower than said metal with said form corresponding in shape to the article to be cast, forming a connecting element from said material to extend between the body and form, embedding the metal body, form and connecting element within an investment compound and arranging them so that the connecting element extends between the body and form, melting and evaporating said material so that the cavity left by the evaporated form is joined to the metal by a communicating opening, and then melting the metal and causing it to flow through said opening into the cavity.

7. The method of casting which comprises providing a body of metal to be melted, molding a form from volatile material having a melting point lower-than said metal with said form correspondingin shape to the article to be cast, forming a connecting element from said material to extend between the body and form, embedding the metal body, form and connecting element within an investment compound and arranging them so that the connecting element extends between the body and form, melting and evaporating said material so that the cavity left by the evaporated form is joined to the metal by a communicating opening, then melting the metal, and then rotating the compound about an axis which causes the molten metal to be thrown centrifugally into the cavity.

8. The method of casting which comprises providing a body of metal to be melted, molding forms from volatile material having a melting point lower than said metal with such forms corresponding in shape to the articles to be cast, embedding the metal and forms within an investment compound with the forms arranged around the metal body in spaced relation and' connecting the body to the forms by connecting elements made from said material, melting and evaporating said material, melting the metal, and rotating the compound and metal so as to cause the molten metal to flow outwardly into the cavities formed by evaporation of said material.

9. The method of casting which comprises forming an annular ring of metal wire, molding forms from a -volatile material having a melting point lower than that of the metal with such forms corresponding in shape to the articles to be cast, embedding the ring and forms within an investment compound with the forms arranged around the exterior of the ring and placing a connecting element made from such material between each form and the ring surface in joining relation thereto, melting and removing said material, then melting the ring and then rotating the parts about the axis of the ring so as to centriiugally force the molten metal into the die cavities.

10. The method of casting which comprises forming an annular ring of metal wire, molding forms from a volatile material having a melting point lower than that of the metal with such forms corresponding in shape to the articles to be cast, embedding the ring and forms within an investment compound with the forms arranged around the exterior of the ring and placing a connecting element made from such material between each form and the ring surface in joining relation thereto, then melting the ring 'by electrical induction, and then rotating the parts so as centrifugally to force the molten metal into the die cavities.

11. The method of casting which comprises providinga body of metal to be melted, molding forms from volatile material having a melting point lower than said metal with such forms corresponding in shape to the articles to be cast, embedding the metal and forms within an investment compound with the forms arranged around the metal body in spaced relation and connecting the body to the forms byconnecting elements made from said material, melting and evaporating said material, melting the metal. and then using fluid under pressure to force the molten metal out into the cavities formed by evaporation of said material.

12. The method of casting which comprises providing a ring of metal to be melted, molding wax forms corresponding to the articles to be cast, attaching each form to the external side of the ring by a radially disposed wax connecting element adhering to the ring and to the form with the forms distributed circumferentially about the ring, forming a wax enlargement at the inner end of each connecting element for receiving a portion of the molten metal when the ring is melted, embedding the wax and metal assembly within an investment compound, melting and evaporating the wax so as to form cavities and a communicating opening between each cavity and the ring and a. pocket at the inner end of the communicating opening, melting the ring, and then rotating the compound about the axis of the ring so as to force the molten metal in each pocket outwardly into the cavity communicating therewith. 1

13. The method of casting which comprises providing a ring of metal to be melted, molding wax forms corresponding totthe articles to be cast, attaching each form to the external side of the ring by a radially disposed wax connecting element adhering to the ring and to the form with the forms distributed circumterentially about the ring, forming a wax enlargement at the inner end of each connecting element in order to provide a pocket for receiving a portion of the in each pocket outwardly into the cavity communicating therewith.

' JOHN D. LEIGHTON. 

